An AgI / layered conjugated polymer carbonitride composite material and its preparation method, a urinary iodine electrochemical sensor and its application

Abstract

This invention discloses a urinary iodine electrochemical sensor based on AgI / layered conjugated polymer carbonitride composite material and its preparation method, belonging to the field of electrochemical sensing technology. The method involves in-situ loading silver iodide (AgI) nanoparticles onto the surface of layered conjugated polymer carbonitrides such as graphitic carbon nitride (g-C3N4) and polytriazineimide (PTI) to construct a composite heterojunction interface with a strong coupling effect. XPS analysis confirmed the directional migration of electrons from carbonitrides to AgI, significantly improving the conductivity and interfacial reaction kinetics of the composite material. Furthermore, this invention addresses the problem that existing AgI / carbonitride composite materials lack customized designs for electrochemical sensing, making them difficult to directly and effectively apply to urinary iodine detection, by optimizing the AgI loading and detection potential. The prepared sensor exhibits extremely high sensitivity to iodine ions, with a detection limit as low as 2.11 μg / L.

Description

Technical Field

[0001] This invention relates to the field of electrochemical sensing technology, and in particular to an AgI / layered conjugated polymer carbonitride composite material and its preparation method, a urinary iodine electrochemical sensor and its application. Background Technology

[0002] Iodine is an essential trace element for the human body, playing a crucial role in the synthesis of thyroid hormones. Adequate iodine intake directly affects metabolism, growth and development, and nervous system health. Iodine is primarily excreted through urine; therefore, urinary iodine concentration is a core indicator recognized by the World Health Organization (WHO) for assessing population iodine nutrition status. WHO guidelines state that the appropriate urinary iodine concentration for adults is 100-199 μg / L, and a concentration below 20 μg / L indicates severe iodine deficiency. Therefore, developing urinary iodine detection technologies that accurately cover a concentration range of 10-1500 μg / L is of great significance for public health monitoring and disease prevention.

[0003] Currently, mainstream methods for detecting urinary iodine have significant shortcomings. Arsenic-cerium catalytic spectrophotometry is cumbersome, requires highly toxic arsenic reagents, and is easily interfered with by high concentrations of chloride ions and other matrices in urine, resulting in insufficient sensitivity at low concentrations. While inductively coupled plasma mass spectrometry offers high precision, its expensive instruments, high maintenance costs, and complex sample preparation hinder its widespread adoption at the grassroots level. In contrast, electrochemical sensing technology has become a research hotspot due to its simple equipment, fast response, and low cost. Among these, silver iodide (AgI)-based electrodes have attracted considerable attention due to their intrinsic high selectivity for iodide ions.

[0004] However, existing AgI-based electrochemical sensors still face challenges. For example, the journal *Analytical Biochemistry* reported that while traditional single-crystal or polycrystalline AgI electrodes possess selectivity, their detection sensitivity is limited by the intrinsic conductivity of the material, with detection limits typically in the tens of μg / L, making it difficult to meet the precise screening needs of individuals with severe iodine deficiency (<20 μg / L). The journal *Electrochimica Acta* reported on improving conductivity and sensitivity through phase modulation (such as the preparation of α-AgI), but effectively suppressing the aggregation of nano-AgI particles and increasing the number of active sites while further improving interfacial electron transport efficiency remains a key bottleneck in constructing high-performance urinary iodine sensors. Therefore, there is an urgent need to develop a novel composite electrode material that combines high conductivity, large active area, and excellent stability.

[0005] It is worth noting that in recent years, composite materials of layered conjugated polymer carbonitrides (such as graphitic carbon nitride g-C3N4, polytriazine imide PTI, etc.) and AgI have been extensively studied in the field of photocatalysis, revealing their potential in light energy conversion. However, applying them to the field of electrochemical sensing is by no means a simple technology transfer.

[0006] First, the two technologies differ fundamentally in their working mechanisms. Photocatalysis relies on the semiconductor band structure to generate charge carriers under illumination, while electrochemical sensing depends on redox reactions (such as AgI + e) ​​that occur at the electrode / electrolyte interface under applied potential. - Ag + I - This means that the optimized band positions (such as conduction band and valence band potentials) in photocatalysis do not directly correspond to the optimal operating potential in electrochemical sensing.

[0007] Secondly, and more importantly, existing AgI / carbonitride composite materials are often designed for photocatalytic properties, making it difficult to directly meet the specific requirements of highly sensitive urinary iodine detection, and they have the following problems: Interface compatibility issues: Although these carbonitrides possess a certain degree of conductivity, their intrinsic conductivity is still far lower than that of metals or carbon-based conductors. If the Fermi level does not match when recombinating with AgI, it may create a potential barrier that hinders electron transfer to the electrode substrate, resulting in a sluggish signal response. Active site shielding problem: In photocatalytically prepared composite materials, AgI is often encapsulated by thick carbonitride layers to maximize light absorption, but this hinders Ig... - The contact and diffusion of ions with AgI active sites during electrochemical detection reduces sensitivity. Unknown issues regarding matrix tolerance: Urine contains large amounts of urea, uric acid, protein, and various salt ions (especially high concentrations of Cl-). - Photocatalysis studies are typically conducted in simple inorganic salt solutions, without considering the interference of complex biological matrices on the stability and selectivity of the aforementioned carbonitride / AgI heterointerface.

[0008] Therefore, there is an urgent need in this field for an AgI / layered conjugated polymer carbonitride composite material and its preparation process that are customized for electrochemical sensing characteristics, in order to solve the key problems such as blocked interfacial electron transport, insufficient exposure of active sites and poor resistance to matrix interference. Summary of the Invention This invention provides an AgI / layered conjugated polymer carbonitride composite material, wherein the layered conjugated polymer carbonitride includes one or more of graphitic carbon nitride, polytriazine imide, or covalent triazine framework, the layered conjugated polymer has a layered stacked structure, and the interlayer spacing between each layer is 0.320-0.350 nm; the AgI is grown in situ in the form of nanoparticles and loaded on the surface and / or interlayer gaps of the layered conjugated polymer carbonitride to form a heterogeneous interface, and the AgI nanoparticle size is 10-50 nm.

[0009] Based on the electrochemical sensing characteristics, this invention designs an AgI / layered conjugated polymer carbonitride composite material, wherein the interlayer spacing of the layered conjugated polymer carbonitride and the morphology of AgI nanoparticles are specifically adjusted so that AgI nanoparticles can be loaded on the surface and / or between the layers of the layered conjugated polymer carbonitride to form a tightly chemically bonded heterogeneous interface.

[0010] This application enables the formation of tightly bonded heterojunctions on both g-C3N4 and PTI, stemming from the fact that both belong to layered conjugated carbonitride polymers and share three key structural features: first, a conjugated π-electron framework composed of tris(triazine) or triazine units, endowing it with a suitable Fermi level to drive interfacial electron transfer; second, a two-dimensional nanosheet morphology, providing a sufficient loading platform for AgI nanoparticles; and third, a surface rich in -NH / NH2 end groups, which can bind with AgI nanoparticles via lone pair electrons. + Coordination occurs, transferring Ag + Oriented anchorage at N sites on the support surface. These three common characteristics ensure the universality of the "pre-adsorption-site nucleation-hydrothermal growth" three-step synergistic preparation method in this application on different carbonitride supports: whether g-C3N4 or PTI, Ag + All of these compounds can first coordinate and anchor to N sites on the surface, then nucleate at specific points on the support surface during the slow addition of KI, and finally form Ag-N chemical bonds with the N sites under hydrothermal conditions, triggering interfacial electron transfer. Therefore, the formation of the tight heterojunction interface does not depend on the unique properties of any one carbonitride, but is the result of the combined effect of the "common surface chemical characteristics of carbonitrides" and the "three-step synergistic preparation method unique to this application," providing a sufficient mechanistic basis for extending the scope of protection to PTI, CTF, and other similar materials.

[0011] Preferably, the mass fraction of AgI in the AgI / layered conjugated polymer carbonitride composite material is 10%-80%. More preferably, the mass fraction of AgI is 50%.

[0012] In exploring the optimal composite ratio of AgI and layered conjugated polymer carbonitrides, this invention further discovered that the electrochemical response intensity of the composite electrode does not have a simple monotonically increasing relationship with the AgI loading, but rather there exists an optimal balance point. When the AgI content is too high or too low, the response signal will significantly decrease; only at a specific ratio can the "number of iodine ion recognition sites" and the "interfacial electron transport channels" be synergistically maximized. This variation cannot be deduced or predicted from existing photocatalysis or electrochemical theories.

[0013] Preferably, the charge transfer resistance of the composite material is 3400-4000 ohms, the redox peak potential difference ΔEp is 0.56-0.58 V, and the electrochemical active area is 0.09-0.13 cm². According to the experiments conducted by the applicant, the charge transfer resistances of the composite material, conventional AgI, and C3N4 material of this invention are as follows: AgI / g-C3N4 / GCE: 3549 ohms; AgI / GCE: 5640 ohms; C3N4 / GCE: 4274 ohms; In addition to the charge transfer resistance (Rct), this application also provides the following data to jointly confirm the functional effect of the heterostructure: (1) The redox peak potential difference ΔEp decreased from 0.58 V of the pure AgI electrode to 0.56 V of the composite electrode, proving that the interfacial electron transfer kinetics are accelerated and the reversibility of the reaction is improved; (2) The electrochemical active area ( Figure 9 (Calculated according to the Randles-Sevcík formula) ECSA reached 0.1156 cm², which is much higher than that of pure AgI electrode (0.0957 cm²), proving that g-C3N4 effectively disperses AgI and increases the number of active sites; (3) At the same concentration, the oxidation peak response current increased from 78.69 μA to 116.55 μA (an increase of 48%), directly proving the interface synergistic sensitization effect. The above data corroborate each other from the three dimensions of electron transfer kinetics, active area and response signal, fully supporting the effectiveness of the heterogeneous interface structure design of this invention.

[0014] To achieve the above objectives, the present invention provides a method for preparing AgI / layered conjugated polymer carbonitride composite materials, comprising the following steps: S1. Prepare a layered conjugated polymer carbonitride support, wherein the layered conjugated polymer carbonitride support has a layered stacked structure and a crystal plane spacing of 0.320-0.350 nm; S2. Weigh the layered conjugated polymer carbonitride carrier prepared in step S1 and dissolve it in deionized water to form a uniform suspension A. S3. Dissolve the silver salt in deionized water to form solution B. Slowly add solution B to suspension A and stir continuously at room temperature for 20-60 minutes to allow the Ag to dissolve.+ It is fully adsorbed onto the surface of layered conjugated polymer carbonitrides; S4. Weigh out an equimolar amount of silver salt and iodine salt, dissolve it in deionized water to form solution C; under light-protected conditions, slowly add solution C dropwise to the mixture described in S3, and continue the reaction for 20-40 min to generate AgI precipitate. S5. The obtained mixture is subjected to hydrothermal reaction, cooled, centrifuged and washed, vacuum dried and ground to obtain AgI / layered conjugated polymer carbonitride composite material.

[0015] Based on an in-depth analysis of the electrochemical sensing mechanism, this invention discovers that for iodide ions (I... - The specific electrochemical sensing of photocatalysis relies on electrode performance that is not simply the sum of the intrinsic properties of the active material. This invention abandons the physical mixing or simple deposition methods commonly used in photocatalysis research, and for the first time proposes a hydrothermal method to grow AgI nanoparticles in situ on the surface of a layered conjugated polymer carbonitride, constructing a tightly chemically bonded heterojunction interface. The layered conjugated polymer carbonitride is selected from one or more of graphitic carbon nitride (g-C3N4), polytriazine imide (PTI), and covalent triazine framework (CTF). This concept aims to simultaneously solve the dual problems of limited active area of ​​a single material and insufficient stability of the modified layer.

[0016] This invention employs a hydrothermal method to enable in-situ growth of AgI on the surface of a layered conjugated polymer carbonitride, forming a tightly chemically bonded heterogeneous interface. In the hydrothermal method, solution B is slowly added to suspension A, and the mixture is continuously stirred at room temperature for 20-60 minutes to allow AgI to grow in situ. + It is fully adsorbed on the surface of layered conjugated polymer carbonitride; in subsequent steps, AgI is generated on the surface of carbonitride through site-specific nucleation, with few free large AgI particles, which can achieve the purpose of fixing AgI between the layered structures and on the surface of the layered conjugated polymer carbonitride carrier. Taking g-C3N4 as an example, X-ray photoelectron spectroscopy (XPS) analysis confirmed that the binding energy of Ag 3d and I 3d shifted negatively by about 3.5 eV, and the binding energy of N 1s shifted positively by about 5.9 eV, indicating that electrons migrated directionally from carbonitrides to AgI (see [link to XPS analysis]). Figure 3 This interfacial electronic coupling effect can prepolarize the electronic states of AgI, reducing Ig - The activation energy of the AgI redox reaction is increased, thereby improving the reversibility of the reaction (ΔEp = 0.56 V for AgI / g-C3N4 / GCE, which is better than ΔEp = 0.58 V for pure AgI / GCE, see [reference]). Figure 4 c, 4d). Electrochemical impedance spectroscopy further showed that the charge transfer resistance (Rct) of the composite material was only 3549 Ω, far lower than the 5640 Ω of the pure AgI electrode (see c, 4d). Figure 4(b) confirms the significant improvement in electron transport efficiency achieved by heterogeneous interfaces.

[0017] Preferably, the preparation of the layered conjugated polymer carbonitride support in step S1, when the layered conjugated polymer carbonitride support is graphitic carbon nitride, specifically includes the following steps: Weigh out the melamine precursor and place it in a covered ceramic crucible. Heat it in a muffle furnace and calcine it at a constant temperature. After the reaction is complete, cool it naturally to room temperature to obtain a yellow block product. Grind it into powder to obtain g-C3N4 nanosheet powder. When the layered conjugated polymer carbonitride support is polytriazine imide, the specific steps include: Weigh out the melamine precursor and LiCl / KCl eutectic and place them in an agate mortar. Grind and mix thoroughly and then transfer to a covered ceramic crucible. Place the crucible in a tube furnace and heat and calcine at a constant temperature under a N2 atmosphere. After the reaction is complete, allow it to cool naturally to room temperature. Wash the product repeatedly with deionized water to remove residual molten salt. Then dry it in an oven and grind it into powder to obtain polytriazine imide powder.

[0018] Preferably, the silver salt in step S2 is silver nitrate, and the iodine salt in step S3 is potassium iodide; The dissolution and dispersion in step S2 is performed by ultrasonic dispersion. The hydrothermal reaction in step S5 is as follows: the obtained mixture is completely transferred to a hydrothermal reactor lined with polytetrafluoroethylene, sealed, and placed in an oven for reaction. The reaction temperature in the oven is 160-200℃, and the reaction time is 8-16h. The drying temperature is 50-80℃.

[0019] To achieve the above objectives, the present invention provides a urinary iodine electrochemical sensor, including a working electrode, the surface of which is modified with the AgI / layered conjugated polymer carbonitride composite material described above. The substrate of the working electrode is selected from one or more of glassy carbon electrode, screen-printed electrode, ITO conductive glass, carbon paper or metal electrode.

[0020] Preferably, when the working electrode is a glassy carbon electrode, the composite material is drop-coated onto the surface of the working electrode using Nafion solution; when the working electrode is a screen-printed electrode, the composite material is fixed onto the surface of the working electrode by drop coating or printing.

[0021] To achieve the above objectives, the present invention provides an application of the aforementioned composite material or the aforementioned urinary iodine electrochemical sensor in detecting the concentration of iodine ions in a urine sample.

[0022] Preferably, the detection of iodide ion concentration in the urine sample using the aforementioned urinary iodine electrochemical sensor includes the following steps: The working electrode, reference electrode, and counter electrode of the urinary iodine electrochemical sensor constitute a three-electrode system; Electrochemical detection was performed in a phosphate buffer solution with a pH of 6.5–7.5, at an applied detection potential of 0.64–0.72 V. The concentration of iodine ions in the urine sample was quantitatively calculated by comparing the recorded current response value with the standard curve.

[0023] Based on the understanding of the above-mentioned interfacial electronic structure characteristics, this invention further optimizes the working detection potential. Taking g-C3N4 as an example, by comparing the responses at three potentials of 0.64 V, 0.68 V, and 0.72 V using the chronoamperometry method, the applied potential range was determined to be 0.64-0.72 V, preferably 0.68 V, at which point the sensitivity reaches 6.07 μA / μg. - ¹ L cm - ². At this potential, the electron transfer effect from carbonitrides to AgI causes AgI to... - The electrochemical oxidation activity reached its optimal level.

[0024] The above-described solution of the present invention has the following beneficial effects: (1) This invention constructs a tightly chemically bonded heterogeneous interface by in-situ growing AgI nanoparticles on a two-dimensional support of layered conjugated polymer carbonitrides (such as g-C3N4, PTI, CTF, etc.). This structural design simultaneously solves the problems of easy aggregation and limited active area of ​​single AgI materials, as well as the shortcomings of weak interfacial bonding and low electron transport efficiency in traditional physical mixing methods. XPS confirmed that electrons are directionally transferred from carbonitrides to AgI, and electrochemical impedance spectroscopy showed that the charge transfer resistance (Rct) of the composite material was only 3549 Ω, which is significantly lower than that of the pure AgI electrode (5640 Ω), and the electrochemical active area (ECSA) was as high as 0.1156 cm². In addition, this invention expands the support material from single g-C3N4 to layered conjugated polymer carbonitrides such as PTI and CTF. By utilizing the common two-dimensional layered structure and tunable electronic properties of these materials, multiple optional platforms are provided for the uniform dispersion of AgI nanoparticles and the construction of heterogeneous interfaces, thus broadening the applicability of the material system.

[0025] (2) Through systematic experiments, this invention reveals an important principle of AgI / layered conjugated polymer carbonitride composite materials in iodide ion electrochemical sensing: the relationship between electrode response intensity and AgI loading is not monotonically linear, but rather there exists an optimal balance point. At this specific ratio, the "number of iodide ion recognition sites" and the "interfacial electron transport channels" are synergistically maximized; deviating from this ratio results in a significant performance degradation. This discovery provides a basis for the rational design of similar composite sensing materials.

[0026] (3) Based on the above-mentioned material and structural advantages, the sensor constructed in this invention achieves excellent detection performance. Its detection linearity range is 5-1500 μg / L, the detection limit is as low as 2.11 μg / L, and the sensitivity is as high as 6.07 μA / μg. - ¹ L cm - ² It accurately covers all iodine deficiency, normal, and excess ranges as defined by the WHO, and is especially effective in identifying people with severe iodine deficiency (<20 μg / L).

[0027] (4) This sensor is effective against common high-concentration interfering substances in urine (such as Cl). - It exhibits good tolerance to substances such as urea and creatinine (at concentrations up to 1000 times higher than iodide ions), with response current changes of less than 3%. The spiked recoveries in simulated urine samples range from 97.27% to 100.45%, and it demonstrates good repeatability (RSD = 2.11%), reproducibility (RSD = 2.42%), and long-term stability (60-day RSD = 1.77%), indicating high accuracy and reliability in complex biological matrices.

[0028] (5) This invention provides a highly versatile sensor fabrication method. The hydrothermal in-situ growth process is not only applicable to systems using g-C3N4 as a carrier, but can also be extended to other layered conjugated polymer carbonitrides such as PTI and CTF; the working electrode substrate is not limited to glassy carbon electrodes, but can also use screen-printed electrodes, ITO conductive glass, or carbon paper, etc. This versatility of the method allows this invention to flexibly select materials and substrates according to different application scenarios and cost requirements, and has good industrialization prospects. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 The flowchart shows the preparation process of the AgI / g-C3N4 / GCE composite electrode. Figure 2 SEM images of (a) g-C3N4, (b) AgI and (c) AgI / g-C3N4 composites, and (dh) corresponding elemental distribution maps; Figure 3 High-resolution XPS fine spectra of AgI / g-C3N4 composite material (a) Ag 3d, (b) I 3d, (c) N 1s and (d) C 1s; Figure 4 In (a), GCE, g-C3N4 / GCE, AgI / GCE, and AgI / g-C3N4 / GCE electrodes were used at 100 μg L⁻¹. -1 (a) CV curves in KI solution; (b) EIS spectra of different electrodes; (c) AgI / GCE electrode in blank electrolyte and 100 μg L -1 CV curves in KI solution; (d) shows the AgI / g-C3N4 / GCE electrode in blank electrolyte and 100 μg L... -1 CV curve in KI solution; Figure 5 (a) shows electrodes prepared from composite materials with different AgI contents at 100 μg L⁻¹ - ¹ CV curve in KI solution; (b) shows the corresponding oxidation peak response current curve and bar chart; Figure 6 (a) shows the chronoamperometry of KI detection using the AgI / g-C3N4 / GCE electrode at potentials of 0.64 V, 0.68 V, and 0.72 V; (b) shows the calibration curve of KI concentration as a function of ampere response; (c) shows the chronoamperometry of KI detection using the AgI / g-C3N4 / GCE electrode at potential of 0.68 V; and (d) shows the calibration curve of KI concentration as a function of ampere response. Figure 7 (a) shows one electrode pair with 10 cups of 50 μg / L. -1 (a) Electrochemical response current of KI solution; (b) 50 μg L of solution from 10 AgI / g-C3N4 / GCE electrode pairs. -1 (c) Electrochemical response current of KI solution; (d) Long-term stability curve of AgI / g-C3N4 / GCE electrode; Figure 8 (a) shows the effect of various interfering ions on the detection of KI by the AgI / g-C3N4 / GCE electrode; (b) shows the corresponding bar chart of the interference experiment. Figure 9 (a) shows the CV curves of the AgI / GCE electrode at different scan rates; (b) shows the linear relationship between the oxidation peak current of the GCE electrode and the square root of the scan rate; (c) shows the CV curves of the AgI / g-C3N4 / GCE electrode at different scan rates; and (d) shows the linear relationship between the oxidation peak current of the C3N4 / GCE electrode and the square root of the scan rate. Figure 10 XRD patterns of g-C3N4, AgI, and AgI / g-C3N4(x) composites. Detailed Implementation

[0031] To make the technical problems, solutions, and advantages of this invention clearer, a detailed description will be provided below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0032] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0033] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a locking connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0034] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0035] Example 1: Electrochemical sensor based on AgI / g-C3N4 and its preparation This embodiment provides a method for preparing AgI / layered conjugated polymer carbonitride composite materials, the overall preparation flow chart of which is shown below. Figure 1 As shown; Synthesis of g-C3N4 support: 10g of melamine precursor was weighed and placed in a covered ceramic crucible. The temperature was increased to 550℃ in a muffle furnace at a rate of 2℃ / min, and calcined at this temperature for 4 hours. After the reaction was completed, the mixture was naturally cooled to room temperature to obtain a yellow blocky product. This product was then ground into powder to obtain g-C3N4 nanosheet powder.

[0036] Synthesis of AgI / g-C3N4 composite material: (1) Weigh 1.0g of the above-synthesized g-C3N4 powder, add it to 10mL of deionized water, and ultrasonically disperse it for 1h to form a uniform suspension A.

[0037] (2) Dissolve 0.72g AgNO3 in 10mL of deionized water to form solution B. Slowly add solution B to suspension A and stir continuously for 30min to allow AgNO3 to dissolve. + It is fully adsorbed on the surface of g-C3N4.

[0038] (3) Weigh an equimolar amount (about 0.71 g) of KI and dissolve it in 10 mL of deionized water to form solution C. Under light-protected conditions, slowly add solution C dropwise to the above mixture and continue the reaction for 30 min to generate AgI precipitate.

[0039] (4) Transfer all the obtained mixture to a hydrothermal reactor lined with polytetrafluoroethylene, seal it and place it in an oven at 180°C for 12 hours.

[0040] (5) After the reaction is completed, the product is cooled naturally, centrifuged to separate the product, and washed several times with deionized water and anhydrous ethanol. Finally, it is dried under vacuum at 60°C and ground to obtain AgI / g-C3N4 composite material powder.

[0041] In the obtained AgI / g-C3N4 composite powder, g-C3N4 exhibits a layered stacked structure, with XRD (002) peaks showing an interplanar spacing of approximately 0.326 nm. AgI is loaded in the form of nanoparticles (particle size approximately 10-50 nm) on the surface and / or interlayer spaces of g-C3N4 nanosheets, forming a tightly chemically bonded heterogeneous interface. The composite material has a charge transfer resistance of 3549 ohms, a redox peak potential difference ΔEp of 0.56 V, and an electrochemically active area of ​​0.1156 cm².

[0042] This embodiment can form a tightly chemically bonded heterogeneous interface, the mechanism of which lies in the synergistic effect of three steps: "stepwise adsorption-precipitation-hydrothermal in-situ growth-interfacial electron self-transfer". First, Ag... + Pre-stir with g-C3N4 suspension for 30 min to allow Ag to... + AgI is fully adsorbed onto the N sites on the surface of g-C3N4 through electrostatic and coordination interactions. Subsequently, KI is slowly added dropwise, causing AgI to nucleate and precipitate at specific sites on the g-C3N4 surface, rather than nucleating freely in solution. Next, the mixture is sealed in a hydrothermal reactor and subjected to a hydrothermal reaction at 180°C and autogenous pressure. The high temperature and pressure environment provides sufficient energy to promote the rearrangement and growth of AgI grains on the g-C3N4 surface, resulting in Ag-N chemical bonds between AgI and the N sites, forming a tight heterogeneous interface. Based on this, the Fermi level difference between g-C3N4 and AgI drives the directional migration of electrons from g-C3N4 to AgI (XPS confirms a decrease in Ag 3d and I 3d binding energies and an increase in N1s binding energy), forming a steady-state interfacial electron transfer effect.

[0043] Electron microscopy and elemental distribution analysis were performed on the g-C3N4, AgI, and AgI / g-C3N4 composite materials in this embodiment. Figure 2 The images are: (a) SEM images of g-C3N4, (b) AgI, and (c) AgI / g-C3N4 composite materials, and (dh) corresponding elemental distribution maps; it can be seen that AgI grows in situ in the form of nanoparticles and is loaded on the surface and / or between the layers of the layered conjugated polymer carbonitrides; the size of the AgI nanoparticles can be determined by the SEM images ( Figure 2 Characterization. SEM showed that AgI particles were uniformly distributed on the C3N4 surface, with a particle size of approximately 10-50 nm, exhibiting nanoscale dispersion.

[0044] Figure 3 High-resolution XPS fine spectra of (a) Ag 3d, (b) I 3d, (c) N 1s and (d) C 1s of the AgI / g-C3N4 composite material in this embodiment; X-ray photoelectron spectroscopy (XPS) analysis confirmed that the binding energy of Ag 3d and I 3d shifted negatively by about 3.5 eV and the binding energy of N 1s shifted positively by about 5.9 eV, indicating that electrons migrated directionally from carbonitrides to AgI; Figure 10 XRD patterns of g-C3N4, AgI, and AgI / g-C3N4(x) composites are shown. The interlayer spacing can be calculated from the XRD data. The (002) characteristic diffraction peak of g-C3N4 is located at approximately 27.5°, and the interlayer spacing is calculated to be approximately 0.326 nm according to the Bragg equation. After AgI loading, the (002) peak of g-C3N4 is basically maintained, indicating that the layered stacking structure is preserved.

[0045] Preparation of AgI / g-C3N4 / GCE working electrode: Weigh 20 mg of the AgI / g-C3N4 composite material powder prepared above and add it to a mixture containing 950 μL of deionized water and 50 μL of 5% Nafion solution. Disperse the mixture ultrasonically for 1 h to obtain a homogeneous slurry. Use a micropipette to transfer 20 μL of the slurry and uniformly drop it onto the surface of a pretreated glassy carbon electrode (GCE). Bake under a 250 W infrared lamp until completely dry to obtain the AgI / g-C3N4 / GCE modified electrode.

[0046] Electrochemical detection: A standard three-electrode system was employed, with AgI / g-C3N4 / GCE as the working electrode, Ag / AgCl as the reference electrode, and a Pt sheet as the counter electrode. The detection medium was 0.05M phosphate-buffered saline (PBS) at pH 7.0. Detection was performed using cyclic voltammetry (CV) or chronoamperometry (it), with an applied potential of 0.68V. Different concentrations of potassium iodide (KI) standard solution were continuously added to the buffer solution, and the resulting current responses were recorded to plot a current-concentration standard curve, thereby enabling the quantification of iodide ion concentration in unknown samples.

[0047] Figure 4 In (a), GCE, g-C3N4 / GCE, AgI / GCE, and AgI / g-C3N4 / GCE electrodes were used at 100 μg L⁻¹. -1 (a) CV curves in KI solution; (b) EIS spectra of different electrodes; (c) AgI / GCE electrode in blank electrolyte and 100 μg L -1 CV curves in KI solution; (d) shows the AgI / g-C3N4 / GCE electrode in blank electrolyte and 100 μg L⁻¹ solution. -1 CV curve in KI solution; By adjusting the amount of AgNO3 and KI added in steps (2) and (3), the mass fraction of AgI in the composite material can be controlled. After further adjusting the mass fraction of AgI based on the scheme of Example 1, electrodes prepared from composite materials with different AgI contents were tested. Figure 5 (a) shows electrodes prepared from composite materials with different AgI contents at 100 μg L⁻¹ - ¹ CV curve in KI solution; (b) is the corresponding oxidation peak response current curve and bar chart; it can be seen that the performance is optimal when the mass fraction of AgI is 50%; Optimization of detection potential Based on the understanding of the above-mentioned interfacial electronic structure characteristics, this invention further optimizes the working detection potential. Taking g-C3N4 as an example, by comparing the responses at three potentials of 0.64 V, 0.68 V, and 0.72 V using the chronoamperometry method, the applied potential range was determined to be 0.64-0.72 V, preferably 0.68 V, at which point the sensitivity reaches 6.07 μA / μg. - ¹ L cm - ². At this potential, the electron transfer effect from carbonitrides to AgI causes AgI to... - The electrochemical oxidation activity reached its optimal level.

[0048] Figure 6(a) shows the chronoamperometry of KI detection using the AgI / g-C3N4 / GCE electrode at potentials of 0.64 V, 0.68 V, and 0.72 V; (b) shows the calibration curve of KI concentration as a function of ampere response; (c) shows the chronoamperometry of KI detection using the AgI / g-C3N4 / GCE electrode at potential of 0.68 V; (d) shows the calibration curve of KI concentration as a function of ampere response. Its detection linear range is 5-1500 μg / L, with a detection limit as low as 2.11 μg / L and a sensitivity as high as 6.07 μA / μg. - ¹ L cm - ² It accurately covers all iodine deficiency, normal, and excess ranges as defined by the WHO, and is especially effective in identifying people with severe iodine deficiency (<20 μg / L).

[0049] Figure 7 (a) shows one electrode pair with 10 cups of 50 μg / L. -1 (a) Electrochemical response current of KI solution; (b) 50 μg L of solution from 10 AgI / g-C3N4 / GCE electrode pairs. -1 (c) Electrochemical response current of KI solution; (d) Long-term stability curve of AgI / g-C3N4 / GCE electrode; Figure 8 (a) shows the effect of various interfering ions on the detection of KI by the AgI / g-C3N4 / GCE electrode; (b) shows the corresponding bar chart of the interference experiment; this sensor is effective against common high-concentration interfering substances in urine (such as Cl). - It exhibited good tolerance to substances such as urea and creatinine (at concentrations up to 1000 times higher than iodide ions), with response current changes of less than 3%. The spiked recoveries in simulated urine samples ranged from 97.27% to 100.45%, and it demonstrated good repeatability (RSD = 2.11%), reproducibility (RSD = 2.42%), and long-term stability (60-day RSD = 1.77%). Figure 9 (a) shows the CV curves of the AgI / GCE electrode at different scan rates; (b) shows the linear relationship between the oxidation peak current of the GCE electrode and the square root of the scan rate; (c) shows the CV curves of the AgI / g-C3N4 / GCE electrode at different scan rates; (b) shows the linear relationship between the oxidation peak current of the g-C3N4 / GCE electrode and the square root of the scan rate.

[0050] Example 2: Electrochemical Sensor Based on AgI / PTI and Its Fabrication To demonstrate that the technical solution of the present invention is also applicable to other layered conjugated polymer carbonitrides, this embodiment uses polytriazine imide (PTI) as a carrier for illustration.

[0051] Synthesis of PTI vectors: Melamine and LiCl / KCl eutectic salt (molar ratio approximately 1:4) were placed in an agate mortar and thoroughly ground and mixed. The mixture was then transferred to a covered ceramic crucible, which was placed in a tube furnace and calcined at 550°C for 4 hours under a N2 atmosphere. After the reaction was completed, the mixture was allowed to cool naturally to room temperature. The product was repeatedly washed with deionized water to remove residual molten salt, and then dried in an oven and ground into powder to obtain PTI powder.

[0052] Synthesis of AgI / PTI composite materials: Referring to step 2 of Example 1, g-C3N4 was replaced with an equal mass of PTI powder. Since both PTI and g-C3N4 are layered conjugated polymeric carbonitrides with similar chemical compositions and electronic structures, those skilled in the art have reason to believe that the hydrothermal in-situ growth method can uniformly load AgI onto the PTI surface and form a tight heterojunction interface.

[0053] Preparation and testing of working electrodes: The AgI / PTI modified electrode was prepared according to steps 3 and 4 of Example 1. Based on the "static interface electronic coupling" mechanism revealed in this invention, the AgI / PTI composite material is expected to exhibit good electrochemical response characteristics to iodine ions, achieving highly sensitive detection.

[0054] Example 3: Electrochemical Sensor Based on AgI / CTF and Its Fabrication To further demonstrate that the technical solution of the present invention is applicable to all the claimed layered conjugated polymer carbonitrides, this embodiment uses a covalent triazine framework (CTF) as a carrier for illustration.

[0055] Synthesis of CTF vectors: 1,4-Dicyanobenzene (DCB) and anhydrous ZnCl2 (mass ratio 1:5) were thoroughly ground and mixed, and calcined at 400℃ in a muffle furnace for 40 h. After washing and drying, CTF powder was obtained.

[0056] Synthesis of AgI / CTF composite material: Referring to step 2 of Example 1, g-C3N4 was replaced with an equal mass of CTF powder. Since CTF, g-C3N4, and PTI are all layered conjugated polymeric carbonitrides with similar chemical compositions and electronic structures, those skilled in the art have reason to believe that the hydrothermal in-situ growth method can uniformly load AgI onto the CTF surface and form a tight heterojunction interface.

[0057] Preparation and testing of working electrodes: The AgI / CTF modified electrode was prepared according to steps 3 and 4 of Example 1. Based on the "static interface electronic coupling" mechanism revealed in this invention, the AgI / CTF composite material is expected to exhibit good electrochemical response characteristics to iodine ions, achieving highly sensitive detection.

Claims

1. An AgI / layered conjugated polymer carbonitride composite material, characterized in that, The layered conjugated polymer carbonitride includes one or more of graphitic carbon nitride, polytriazine imide, or covalent triazine framework. The layered conjugated polymer has a layered stacked structure with a crystal plane spacing of 0.320-0.350 nm. The AgI is grown in situ in the form of nanoparticles and loaded on the surface and / or interlayer gaps of the layered conjugated polymer carbonitride to form a heterogeneous interface. The AgI nanoparticles have a size of 10-50 nm.

2. The composite material as described in claim 1, characterized in that, The mass fraction of AgI in the AgI / layered conjugated polymer carbonitride composite material is 10%-80%.

3. The composite material as described in claim 1, characterized in that, The composite material has a charge transfer resistance of 3400-4000 ohms, a redox peak potential difference ΔEp of 0.56-0.58 V, and an electrochemical active area of ​​0.09-0.13 cm².

4. A method for preparing the AgI / layered conjugated polymer carbonitride composite material as described in any one of claims 1-3, characterized in that, Includes the following steps: S1. Prepare a layered conjugated polymer carbonitride support, wherein the layered conjugated polymer carbonitride support has a layered stacked structure and a crystal plane spacing of 0.320-0.350 nm; S2. Weigh the layered conjugated polymer carbonitride carrier prepared in step S1 and dissolve it in deionized water to form a uniform suspension A. S3. Dissolve the silver salt in deionized water to form solution B. Slowly add solution B to suspension A and stir continuously at room temperature for 20-60 minutes to allow the Ag to dissolve. + It is fully adsorbed onto the surface of layered conjugated polymer carbonitrides; S4. Weigh out an equimolar amount of silver salt and iodine salt, and dissolve it in deionized water to form solution C; Under light-protected conditions, solution C is slowly added dropwise to the mixture described in S3, and the reaction continues for 20-40 minutes to generate AgI precipitate. S5. The obtained mixture is subjected to hydrothermal reaction, cooled, centrifuged and washed, vacuum dried and ground to obtain AgI / layered conjugated polymer carbonitride composite material.

5. The preparation method according to claim 4, characterized in that, The preparation of the layered conjugated polymer carbonitride support in step S1, when the layered conjugated polymer carbonitride support is graphitic carbon nitride, specifically includes the following steps: Weigh out the melamine precursor and place it in a covered ceramic crucible. Heat it in a muffle furnace and calcine it at a constant temperature. After the reaction is complete, cool it naturally to room temperature to obtain a yellow block product. Grind it into powder to obtain g-C3N4 nanosheet powder. When the layered conjugated polymer carbonitride support is polytriazine imide, the specific steps include: Weigh out the melamine precursor and LiCl / KCl eutectic and place them in an agate mortar. Grind and mix thoroughly and then transfer to a covered ceramic crucible. Place the crucible in a tube furnace and heat and calcine at a constant temperature under a N2 atmosphere. After the reaction is complete, allow it to cool naturally to room temperature. Wash the product repeatedly with deionized water to remove residual molten salt. Then dry it in an oven and grind it into powder to obtain polytriazine imide powder.

6. The preparation method according to claim 4, characterized in that, The silver salt mentioned in step S2 is silver nitrate, and the iodine salt mentioned in step S3 is potassium iodide; The dissolution and dispersion in step S2 is performed by ultrasonic dispersion. The hydrothermal reaction in step S5 is as follows: the obtained mixture is completely transferred to a hydrothermal reactor lined with polytetrafluoroethylene, sealed, and placed in an oven for reaction. The reaction temperature in the oven is 160-200℃, and the reaction time is 8-16h. The drying temperature is 50-80℃.

7. A urinary iodine electrochemical sensor, characterized in that, Includes a working electrode, the surface of which is modified with the AgI / layered conjugated polymer carbonitride composite material as described in any one of claims 1 to 3; The substrate of the working electrode is selected from one or more of glassy carbon electrode, screen-printed electrode, ITO conductive glass, carbon paper or metal electrode.

8. The urinary iodine electrochemical sensor as described in claim 7, characterized in that, When the working electrode is a glassy carbon electrode, the composite material is drop-coated onto the surface of the working electrode using Nafion solution; when the working electrode is a screen-printed electrode, the composite material is fixed onto the surface of the working electrode by drop coating or printing.

9. The application of a composite material as described in any one of claims 1 to 3 or the urinary iodine electrochemical sensor as described in claim 7 or 8 in detecting the concentration of iodine ions in a urine sample.

10. The application as described in claim 9, characterized in that, The detection of iodide ion concentration in a urine sample using the urinary iodine electrochemical sensor as described in any one of claims 7-8 includes the following steps: The working electrode, reference electrode, and counter electrode of the urinary iodine electrochemical sensor constitute a three-electrode system; Electrochemical detection was performed in a phosphate buffer solution with a pH of 6.5–7.5, at an applied detection potential of 0.64–0.72 V. The concentration of iodine ions in the urine sample was quantitatively calculated by comparing the recorded current response value with the standard curve.

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